This invention relates to the field of devices for securing motorcycle front forks to the head tube of the motorcycle frame, and in particular, to an improved yoke for the mounting of front forks to the head tube.
As seen in FIGS. 1 and 2, it is known in the prior art to use angularly shaped sharp or hard-edged yokes for pivotally mounting motorcycle front forks to the head tube of the motorcycle frame. For use on motorcycles such as Harley Davidson(trademark) motorcycles, such components may be purchased from vendors such as Perse Performance(trademark) of Englewood, Colo., for example components from that vendor referred to as Triple Trees(trademark). Conventionally yokes such as the Triple Tree kits marketed by Perse Performance(trademark) are manufactured as a kit of separate components that must be assembled to form the yoke. The yokes clamp around the outside of the fork tubes. The clamping of the yokes around the outside of the fork tubes may reduce the aesthetic appeal of the motorcycle. Further, it introduces the potential for a loss of rigidity of the yoke, such a loss of rigidity being undesirable in that the front wheel of the motorcycle is cantilevered from the yoke at the end of relatively long forks and thus subject to considerable force, bending moment and vibration.
There is a significant aftermarket in customizing motorcycles such as Harley Davidson(trademark) motorcycles. One such example is the subject of FIG. 2, being a customized motorcycle used for display at motorcycle shows and the like. As may be seen, the customizing of the motorcycle results in a significantly rounded, flowing design where the conventional teardrop shape of the fuel tank is modified so that the fuel tank flows conformably into the seat pad saddle which itself then slows curvaceously into the swell of the rust fender. This lends the motorcycle a low elegantly curved profile. The curved low side-on profile is complemented by the use of aft-swept arcuately curved handlebars sweeping back from where they are mounted to the yoke immediately adjacent the head tube of the frame to which the motor and lower decorative fairings or cowlings are mounted. The yoke conventionally supports the forward extending forks, the front wheel and front fender mounted cantilevered on the distal end of the forks. Conventionally, the headlight is mounted to, so as to extend forwardly from between the uprights of the yoke.
The use of a prior art yoke on such a customized motorcycle, or for that matter other customized motorcycles which have rearwardly flowing curved lines in side-on profile, rather harshly interrupts the flowing lines of the profile due to the conventional hard-edged clamping of the corners of the generally triangular mounting plates around the exterior surface of the upper ends of the fork tubes or posts.
Thus in the present invention it is an object to provide a yoke which has, contrary to the motorcycle prior art of which applicant is aware, modular butt-jointed cross-bearing members or arches, where the yoke smoothly and aerodynamically curves rearwardly so as to complement the rearward flowing lines of the adjacent teardrop-shaped fuel tank on the motorcycle when the yoke is mounted to the head tube.
In summary the present invention is a modular butt-jointed front fork yoke for a motorcycle. The yoke may include upper and lower arches extending between a parallel pair of posts wherein the lower arch is butt-jointed to the pair of posts. Each post has an upper end and an opposite lower end. The upper arch extends from and between each upper end of the posts. Each upper end forms an impost at opposite ends of the upper arch.
The lower arch parallels the upper arch and is mounted to, so as to extend between, the lower ends of the pair of posts or adjacent the lower ends of the posts. The upper and lower arches each have a vertice lying on or adjacent an axis of rotation of the yoke when the yoke is mounted to a motorcycle frame so that a head tube of the frame is coaxial with the axis of rotation and is mountable snugly between the vertices of the upper and lower arches. The upper and lower arches each form a corresponding concavity under each arch which opens downwardly towards the lower ends of the posts.
The imposts form a pair of rounded-over shoulders between the upper arch and the posts. The shoulders are rounded in a plane containing the pair of posts so as to smoothly blend outer surfaces of the upper ends of the posts into outer surfaces of opposite ends of the upper arch, and are rounded-over between the front and rear of the yoke.
The pair of posts and the arches collectively have a front face, for facing forwardly from the motorcycle when the yoke is mounted to the motorcycle frame, and an opposite rear face. The arches have corresponding rear surfaces. Protrusions on the rear surfaces of the arches are curved so as to smoothly protrude rearwardly adjacent the vertices of the arches. The protrusions are adapted for vertically aligned mounting of the head tube therebetween. The front face is smoothly rounded over toward the rear face around forwardly exposed edges of the posts and the arches. The shoulders are rounded so as to smoothly blend from the front face at the upper ends of the posts, upwardly into the opposite ends of the upper arch and rearwardly so as to round smoothly into the rear face. The yoke is adapted so that the front face rakes, and is curved upwardly, aft when the yoke is mounted on the motorcycle frame, whereby a side profile of the yoke smoothly and aerodynamically blends into aft flowing curved lines of the motorcycle.
In one embodiment the pair of posts may be a pair of cylinders and the arches may each be generally semi-circular, that is, semi-circular or a lesser segment of a circle. The shoulders may be cupped so that each is shaped in the form of a cup-segment, that is, smoothly rounded as might be a well muscled human shoulder. Thus the arches and the shoulders may each have an upper surface which is rounded from the front face to the rear face of the yoke symmetrically about the above-defined plane, in which case the plane bisects the pair of posts so that longitudinal axes of symmetry of each post lie in the plane.
The lower arch parallels the upper arch and is butt-joint mounted to the posts or uprights at each end of the lower arch, so as to extend between the lower ends of the posts or adjacent the lower ends of the posts.
In one embodiment not intended to be limiting, each post has a symmetrical aperture in a sidewall thereof, and inside each post is a ledge adjacent the lower end of the post such that the ledge is below the aperture. Each post has an outer diameter, measured between the outer edges of one end of the post, and an inner diameter, measured between the inner edges of that end of the post.
Two hollow collars or cylinders are provided, each having an upper end and a lower end. Each cylinder is open at both ends. Each cylinder has an asymmetrical aperture, that is, a cammed aperture having an asymmetric cam surface. Each cylinder has an outer diameter, measured between the outer edges of one end of the cylinder, and an inner diameter, measured between the inner edges of that end of the cylinder. The outer diameter of each cylinder approximates, that is, is slightly less than the inner diameter of each post for snug flush sliding fitment of a cylinder into a corresponding post.
Thus, when a cylinder is inserted into each post, each cylinder rests on the ledge inside the corresponding post so as to align the cammed aperture on the cylinder with the symmetrical aperture in the post. A corresponding cammed nut is mounted into the cammed aperture so as to mate the asymmetrically cammed surfaces, thereby preventing rotation of the nut in the cammed aperture. Bolts are inserted through bolt-holes in the ends of the lower arch, through the symmetric apertures in the posts so as to threadably engage the cammed nuts mounted in the cammed apertures in the cylinders. Tightening the bolts draws the ends of the lower arch rigidly onto the opposed facing outer surfaces of the pair of posts.